The present invention relates to magnetic hard disk drives. More specifically, the present invention relates to a method and apparatus for grounding a magnetic recording head that may avoid the use of a conductive adhesive.
A disk drive for data recording uses magnetic recording heads for writing and reading data on recording disks. The recording heads are built on a substrate, called a wafer, which is made of electrically conductive material, such as AlTiC, with processes similar to those for semiconductor devices. Gold pads on the external surface of the recording head are electrically connected to the recording devices through internal electrical paths built during the wafer-level processes. The wafer is then sliced into rectangular pieces with an individual recording head on each piece with the substrate attached, which is called a slider. Afterwards, the slider is mounted on a suspension. The assembly is called a head gimbal assembly, or HGA. The slider is then bonded on the suspension with glues, including a conductive glue to form an electrical connection between the substrate and a stainless steel component of the suspension. Additional electrical connections are made between the gold pads on the recording head and metal trace lines on the suspension with methods including ultrasonic bonding or soldering. Finally, the HGA is assembled into a hard disk drive device with the suspension traces connected to other electrical components, typically a pre-amplifier, and the stainless steel part of the suspension connected to the electrical ground of the drive.
Generally, there are two types of HGAs—wired and wireless. A wired HGA is one where separate lead wires are connected between the flex circuit of the HSA and the read write head. A wireless HGA is one where conductive traces are integrated with the flexure and provide conductivity between the flex circuit of the HSA and the read write head of the slider. In the art, there are typically two types of wireless suspensions. In the first type, such as trace suspension assemblies (TSAs) and circuit integrated suspension (CISs), traces are built though a subtractive process (e.g., an etching operation) or through an additive process (e.g., a plating or deposition process) on the stainless steel flexure, with an insulative layer between the trace and the flexure. After the traces are set in place, the flexure can then be welded to other parts of the suspension. In the second type, such as flex suspension assemblies (FSAs) and flex on suspension (FOS), the traces are built on an insulation layer and then covered with another insulation layer to form a flex circuit. This circuit is then attached to the suspension with adhesive. Alternatively, an additional metal layer called a ground plane can be attached to the flex circuit before it is adhered to the suspension. In an FSA, the flexure is integrated with a load beam and a mount plate along with the integrated traces for connectivity.
As illustrated in FIG. 1, a head gimbal assembly 40 often provides the slider with multiple degrees of freedom such as vertical spacing, or pitch angle and roll angle, which describe the flying height of the slider. As shown in FIG. 1, a suspension 74 holds the HGA 40 over the moving disk 76 (having edge 70) and moving in the direction indicated by arrow 80. In operation of the disk drive shown in FIG. 1, an actuator 72 moves the HGA over various diameters of the disk 76 (e.g., inner diameter (ID), middle diameter (MD) and outer diameter (OD)) over arc 78.
A preamplifier is typically connected to the head to supply write currents to the write head and receive currents from the read head. The preamplifier resides in a subassembly common referred to as the Actuator Flex Preamp Assembly (AFPA). The preamplifier is usually soldered to a flexible circuit. This flexible circuit provides the areas to which the HGA traces will be connected to complete the circuit connecting the preamplifier to the read and write elements of the head.
The suspension provides two functions: mechanical support and electrical connection between the head and the preamplifier. Rather than using physical wires to connect the head to the preamplifier, metal traces on the suspension are quite often used.
The method of using conductive glue to electrically ground the recording head substrate has many disadvantages. Most of all, the electrical resistance of the conductive glue is unreliable and hard to control. The resistance can be very high and widely variable from part to part during the manufacturing process. In addition, it is difficult to control the flatness of the slider after mounted into the HGA, which is another critical parameter. In addition, to apply and cure the conductive glue in the HGA assembly requires many processes adding to the cost and duration of the manufacturing process.
The use of the stainless steel suspension as the electrical grounding connection between the HGA and the electrical ground provided in the disk drive also may provide disadvantages. The electrical resistance of the stainless steel suspension may vary significantly between such components. If the electrical resistance of the stainless steel suspension is high, then there will be less reliable interfaces with other metal structures in the grounding path (e.g., the actuator).
In view of the above, there is a need for an improved method and apparatus for grounding a read/write head/slider that overcomes the disadvantages of these known systems.